Mordenite which has been loaded with metals such as copper and silver are known to be suitable for use as catalysts for the carbonylation of feedstocks such as methanol, dimethyl ether and dimethyl carbonate to produce the carbonylation products methyl acetate and/or acetic acid.
EP-A-0 596 632 describes a vapour phase process for the carbonylation of methanol to produce acetic acid in the presence of a mordenite loaded with copper, nickel, iridium, rhodium or cobalt catalyst at high temperatures and pressures. The preparation of copper, rhodium and iridium loaded mordenites by wet impregnation of the metal salt solutions is described.
WO 2005/105720 describes a process for production of a carboxylic acid and/or an ester or anhydride thereof by carbonylating an aliphatic alcohol or reactive derivative thereof with carbon monoxide in the substantial absence of halogens in the presence of mordenite loaded with copper, nickel, iridium, rhodium or cobalt and having as framework elements, silicon, aluminium and at least one of gallium, boron and iron at a temperature in the range 250-600° C. and a pressure in the range 10 to 200 bar.
WO 2006/121778 describes a process for the production of a lower alkyl ester of a lower aliphatic carboxylic acid by carbonylating under substantially anhydrous conditions a lower alkyl ether with carbon monoxide in the presence of a mordenite or ferrierite catalyst optionally loaded with copper, nickel, iridium, rhodium, platinum, palladium or cobalt. The preparation of a metal loaded mordenite or ferrierite is not described in WO 2006/121778.
‘Carbonylation of methanol on metal-acid zeolites: Evidence for a mechanism involving a multisite active center’ by T Blasco et al, Angew. Chem. Int Ed. 2007, 46, 3938-3941 describes the ion-exchange of H-mordenite with copper. The amount of copper in the resultant mordenite is stated to be 2.5 wt %.
Metal loaded catalysts are generally expensive to prepare due to the cost of the metal. Thus, there is a need for catalysts which contain a reduced amount of metal but which retain comparable catalytic performance to those containing higher amounts of the same metal.